Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a sequence of a display screen or portion thereof with a graphical user interface showing the new design; and,

FIG. 2 is a second image in the sequence.

The subject matter in the drawings includes a process or period in which an image changes into another image. This process or period forms no part of the claimed design. The dashed broken line showing a display screen or portion thereof is for the purpose of illustrating portions of the article and forms no part of the claimed design. All other broken lines showing text and other elements of the graphical user interface are for the purpose of illustrating portions of the article and forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 